Free piston



May 21, 1963 T. MILTON 3,090,315

FREE PISTON Filed Oct. 20, 1960 2 Sheets-Sheet 1 70 /0/* M/ /fo/7 INVENTOR.

May 21, 1963 T. MILTON 3,090,315

FREE PISTON Filed Oct. 20, 1960 2 Sheets-Sheet 2 Tay/ar /W//Z0/7 INVENTOR.

3,il0,315 FREE PISTQN Tayior Milton, Longview, Tex, assignor to US. industries, inc, New York, NY. Filed Oct. 26, 1969, Se No. 63,925 9 Claims. (*Cl. 1633-52) This invention relates to apparatus for lifting fluid in a Well. More particularly, it relates to an improved free piston for this purpose of the type having an eXpansible packer for forming a seal between the piston body and the inner surface of the well tubing.

It is common practice to employ a free piston for lifting fluid in a well tubing, the piston being driven on its upward stroke by fluid pressure and being returned on its downward stroke by gravity. Frequently, the piston is required to travel the length of the well tubing during its upward and downward strokes, although in some in stances it may travel less than the full length of the tubing in completing its cycle. In any event, in order to prevent slippage and loss of driving pressure fluid between the piston body and well tubing, the piston should be capable of establishing and maintaining a substantially complete pack-otf of the well tubing during lifting opera tions. This not only permits lower injection pressures than are normally required or in the alternative allows more fluid to be lifted at each cycle without increasing injection pressure, but also prolongs the natural flow period of the well when reservoir pressure is utilized to drive the piston on its upward stroke. In addition, a substantially complete pack-off of the well tubing permits lower piston velocities, tends to reduce gas/fluid ratios, and minimizes emulsion forming conditions in the vicinity of the piston.

in order to obtain a complete pack-off of the well tubing, it is necessary to provide means on the piston for establishing and maintaining a substantially fluid-tight seal between the piston body and the inner surface of the Well tubing. Since the well tubing generally does not have a uniform cross section and the body of the piston must be made sufliciently small to freely pass through the tubing, such seal means must be capable of expanding and contracting radially of the piston body to compensate for irregularities in the tubing if a seal is to be maintained as the piston travels therethrough. Ordinary expandible piston ring type seals are not suitable because they tend to hang up at the tubing joints and prevent the piston from performing its intended function. Resilient packers have been used in some cases but they are considered unsatisfactory because, among other reasons, they tend to wear rapidly and have a relatively short service life.

In an attempt to meet these requirements and obtain the desired results, free pistons have been developed having expansible packers consisting of a plurality of radially expansible sealing elements, usually of metal, for forming a seal between the piston body and the inner surface of the well tubing without substantially interfering with the free passage of the piston through the tubing. However, it has been found that these newly developed packers fail to meet these requirements in many respects and therefore cannot obtain the desired results, at least not to the extent considered necessary for efiicient and economical operation. For example, in some pistons the metal sealing elements of the expansible packer wear rapidly and are easily broken, thereby requiring frequent replacement or repair. In other pistons, the sealing elements of the packer are not capable of establishing and maintaining an effective seal and therefore permit excessive slippage and loss of driving pressure fluid between the piston body and the inner surface of the well tubing.

An object of this invention is to provide an improved 7 3,090,315 Patented May 21, 1963 free piston for lifting fluid in a well tubing which obviates the foregoing difliculties and disadvantages.

Another object of the invention is to provide an improved free piston of the type having an expansible packer, the packer being capable of establishing and maintaining a substantially complete pack-off of a well tubing and having a relatively long service life as compared to free piston packers presently being used.

Another object of the invention is to provide an improved free piston having an expansible packer capable of establishing and maintaining a substantially fluid-tight seal between the piston body and the inner surface of a well tubing as the piston travels therethrough, the packer being relatively rugged in construction and trouble free in use as compared to presently known free piston packers.

A particular object of the invention is to provide an improved free piston of the expansible packer type in which the packer includes an outer sealing assembly comprising a plurality of sealing segments for sealably engaging the inner surface of a well tubing over a relatively large area, and an inner back-up assembly for moving the sealing segments outwardly from the piston body into engagement with the well tubing and at the same time sealably bridging between adjacent ones of the sealing segments.

ther objects, advantages and features are inherent and will become apparent upon consideration of the specification, claims, and attached drawings.

In the drawings illustrating one form of the invention with which the foregoing and other objects and advantages can be obtained and wherein like characters are used to designate like parts throughout the several views:

FIG. 1 is a side elevation, partially in cross section, of a free piston constructed according to this invention showing the expansible packer in an expanded condition;

FIG. 2 is an exploded isometric view of a portion of the expansible packer of FIG. 1;

FIG. 3 is a view taken along the line 3-3 of FIG. 1; and

FIG. 4 is a view taken along the line 44 of FIG. 1.

Referring now to the drawings and the form of the invention illustrated, free piston 10 includes a body 11 having a flow passageway 12 formed therein, passageway 12 opening exteriorly of body 11 through ports 13 at a point above expansible packer 14 and opening into valve means 15 at a point below packer 14. Expansible packer 14- and valve means 15 cooperate to provide a substantially complete pack-off of the well tubing (not shown) during lifting operations, expansible packer 14- being capable of establishing and maintaining a substantially fluidtight seal between body 11 and the inner surface of the well tubing as the piston travels therethrough and Valve means 15 being operable to selectively prevent and permit flow of fluid through the piston during its upward and downward strokes, respectively.

Referring first to valve means 15, it will be seen that this component of piston 10 may include a valve cage 16 removably mounted at the lower end of body 11 as by threaded connection 17, cage 16 being provided with ports 18 which communicate through valve chamber 19 with flow passageway 12 when the valve is open to permit fluid to flow through the piston during its downward stroke. A downwardly facing valve seat 26 surrounds flow passageway 12 at the lower end of body 11 and cooperates with valve member 21 for preventing flow of fluid through the piston during its upward stroke. Valve member 21 has a downwardly extending stem portion 22 which is slidably received in axial bore 23 formed in the lower portion of cage 16, stem 22 having a pair of axially spaced part circumferential grooves 24 and 25 which cooperate with spring loaded ball 26 for holding valve lower operating rods 30 and 31, respectively.

member 21 in its open and during the downward and upward strokes of the piston. Ball 26 is mounted in lateral bore 27 formed near the lower end of cage 16 and is urged toward its seated positions in grooves 24 and 25 by spring 28 which is mounted between ball'26 and retainer cap 29. As shown, when valve member 21 is in its closed position seated 011 seat 20 with ball 26 seated in groove 25, the lower end of stem 22 is substantially flush with the lower end of cage 16. However, it will be understood that when valve 21 is in its open position with ball 26 seated in groove 24, the lower portion of stem 22 extends below the lower end of cage 16 a distance substantially equivalent to the distance between grooves 24 and 25. As will be seen,

this provides means for moving valve member 21 from its open to its closed position when the piston reaches the bottom of its downward stroke.

Operating means is provided for moving valve member 21 from its closed to its open position when the piston reaches the top of its upward stroke. As best seen in FIG. 1, such operating means may include upper and Lower operating rod 31 extends axially through flow passageway :12 and engages valve member 21 at its lower end and terminates at its upper end in axial bore 32. Cap 33, mounted on the upper end of rod 31 for sliding movement along bore 32, has an outer upwardly directed shoulder 34 for engaging the lower end of the shock absorber spring 35 and an inner upwardly directed surface 35 for engaging the lower end 37 of upper rod 39 when spring 35 is compressed. Laterally extending arms 38 on rod 31 slidably engage the inner surface of flow passageway 12 for guiding the rod during its'reciprocal movement.

Upper rod 30 is formed on an enlarged diameter 41 intermediate its ends, the upper portion of rod 30 being slidably received in bore 39 and the enlarged portion 41 of rod 30 being slidably received in bore 32. Up wardly directed shoulder 42 on enlarged portion 41 engages shoulder 40 at the lower end of bore 39 for limiting the upward movement of rod 30 While downwardly directed shoulder 43 on enlarged portion 41 engages the upper end of shock absorber spring 35. As

shown, shock absorber spring 35 normally acts to hold the upper and lower operating rods, 30 and 31, in spaced apart relationship and also serves to maintain the lower end of operating rod 31 in engagement with valve member 21.

Turning now to expansible packer 14, it will be seen that this component of piston includes an outer sealing assembly comprising a plurality of arcuate sealing segments 44 (there are four such segments in the embodiment shown) for sealably engaging the inner surface closed positions, respectively,

of the well tubing, and an inner back-up assembly comprising a plurality of arcuate shims 4S (there are also four shims in the embodiment shown) for moving segments 44 outwardly into engagement with the well tubing and at the same time sealing between adjacent ones of the segments. Thus, the outer sealing assembly and the inner back-up assembly of the expansible packer of this invention cooperate to form a substantially fluid-tight seal between piston body 11 and the inner surface of the well tubing, to prevent slippage and loss of driving pressure fiuid therebetween.

Referring now to the outer sealing assembly, each of segments 44, which preferably are made of metal, has a head portion 46 and an axially extending stem portion 47 formed integrally therewith, head portion 46 stantially the length of each segment for engaging and forming a seal with the inner surface of the well tubing.

The edges 56 of each land also act as scrapers to remove paraffin or other deposits from the inner surface of the tubing as the piston travels therethrough.

As best seen in FIGS. 1 and 2, segments 44 surround body 11 and are mounted thereon for limited movement radially of the body, the several segments being arranged in interlocking relationship with the head portion 46 and the stem 47 of adjacent ones of the segments facing in opposite directions. The lateral edges 51 of the head portions of adjacent ones of the segments overlap at all times as indicated at 52, but the longitudinal edges of the head and stem portions of adjacent ones of the segments may have spaces or gaps 53 therebetween, particularly when the segments are moved outwardly from body 11 and away from each other to seal-ably engage the inner surface of the :well tubing. As can be seen in the drawings and as will appear from the explanation to follow, shims 45 of the inner back-up assembly preferably bridge these gaps and also operate to move the segments outwardly from the body.

Each of sealing segments 44 also is provided with tabs 5455 and U-shaped brackets 62-63 at its head and stem ends, respectively. These tabs and U-shaped brackets are received in the annular spaces 56 and 57 formed between body 11 and the downwardly facing skirt 58 on upper retainer ring 59 and the upwardly facing skirt 60 on lower retainer ring 61. The outer surfaces of the tabs are shaped to conform. to the inner surfaces of the skirts, the engagement between these surfaces providing means :for limiting the radially outward movement of the segments as shown in FIG. 1. The U-shaped brackets 62 and 63 on each segment straddle and engage the semicircular shoulders '64 formed in each of retainer rings 59 and 61.

Referring now to the back-up assembly, each of arcuate shims 45, which preferably are made of metal, has a collar 65 intermediate its ends and outwardly turned flanges 66 and 67 at its ends, the outer face of each shim being shaped to conform to the inner surfaces of sealing segments 44. The several shims surround body 11 and are mounted on segments 44 between the segments and the body with the shoulders 65 of the shims being received in the grooves 68 formed along the inner surfaces of the segments and the outwardly turned flanges 66 and 67 of each shim overlying the ends of adjacent ones of the segments between their respective end brackets 62 and 63 (FIG. 2). Thus, the several shims are positioned so that each shim overlies a. gap :73 and bridges between a pair of adjacent ones of the segments. As best seen in FIG. 2, the axis of each shim 45 normally bisects the overlap 52. between the lateral edges of the head portions of adjacent ones of the segments, the shim preferably being sized so that its longitudinal or side edges substantially coincide with the longitudinal axes of said adjacent segments when the packer is retracted. Thus, the area of the outer face of each shim is substantially equal to the area of the inner surface of each sealing segment. Under these circumstances, the side edges of the several shirns will abut one another when the packer is contracted but will be spaced apart only a relatively short distance "when the packer is expanded (see FIGS. 3 and 4). Thus, the shims can be considered as being an expansible sleeve which engages substantially the entire inner surfaces of the sealing segments. This arrangement is preferred since it tends to reduce the rate of wear and likelihood of breakage of the various packer elements and thereby substantially increases the service life of the packer. In addition, this construction and arrangement of the sealing segments and shims increases the sealing efiectiveness of the packer and substantially reduces slippage and loss of rality of springs 69 mounted in recesses 70 formed in the inner surfaces of shims 45 intermediate their ends. The springs act between the shims and body 11 to move the shims radially outwardly from the body and apart from one another into engagement with the inner surfaces of se ments 44. Since the shims are mounted on the segments, the radially outward movement of the shims also operates to move the segments radially outwardly from the body and apart from one another into sealing engagement with the inner surface of the well tubing.

In order to provide a complete understanding of the invention, one method of assembling and operating the piston now will be described. First, piston body 1-1 is secured in an inverted condition and operating rod 30, shock absorber spring 35, operating rod 31, and retainer ring 59 are assembled on the body in their operative positions. One each of springs 69', shims 45, and sealing segments 44 are then assembled and mounted as a unit on body 11 by sliding one end of the segment under the skirt 53 so that its U-shaped end bracket straddles one of shoulders 64 in the retainer ring. This step is repeated until all of the springs, shims, and sealing segments are mounted on me body with one end of the segments of each unit received beneath the skirt 58 with its U-shaped end bracket straddling a shoulder 64 and the several segments being arranged in interlocking relationship as shown. Lower retainer ring 61 is then assembled by slipping its skirt 6t? over the free ends of the several sealing segments so that their U-shaped end brackets straddle shoulders 64 in this ring similarly as in the case of upper retainer ring 59. With the packer thus assembled, valve cage 16, with valve member 21 in the open position, is then made up on body 11 until body key 71 can be inserted into body recess 72 through semicircular slots 73 and 7 4 formed in the upper and lower ends of valve cage 15 md lower retaining ring 61, respectively. There are four each of the slots 73 and 74 in the embodiment shown and of course the several slots should be aligned so that body key 71 can be moved therethrough and into position in body recess "72. Key 71 is held in this position by snap ring 75, the outwmdly turned edges 76 of the ring being received in one of semicircular slots 73 in cage 16.

The assembled piston is now ready for operation within a well tubing. It will be recalled that the valve member 21 is in its open position. Thus, although sealing segments 4 sealably engage the inner surface of the well tubing at all times, the piston drops by gravity through the tubing since any well fluid encountered bypasses the packer through ports 18, valve chamber 19, flow passageway 12 and ports 13. When the piston reaches the bottom of its downward stroke, the lower end of valve stem 22 strikes a bumper device (not shown) which closes valve member 21 and prevents further flow of fluid through the piston to thereby provide a substantially complete pack-off of the well tubing. Driving pressure fluid is then introduced into the tubing at a point below the piston to drive it upwardly and lift the fluid trapped in the well tubing above the piston. When the piston reaches the upper end of its lifting stroke, upper operating rod 3% strikes another bumper device (not shown). This, of course, moves rod downwardly against spring and in turn moves lower operating rod 31 downwardly to open valve member 21 to permit the piston to return by gravity and pick up another load of well fluid.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the r d invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what I claim is:

1. A free piston comprising, in combination, a body having a passageway for fluid therethrough; valve means in the body for controlling flow of fluid therethrough; an expansible packer on the body, said packer including an outer sealing assembly comprising a plurality of interlocking sealing segments mounted for limited movement radially of the body, said sealing segments having spaces between their adjacent longitudinal edges when the packer is expanded, and a separate inner back-up assembly interposed between said body and said sealing segments, said back-up assembly comprising a plurality of arcuate shims having surfaces shaped to conform to the inner surfaces of said sealing segments, the several shims being arranged so that each shim overlies and sealably bridges said space bet-ween adjacent ones of the sealing segments during expansion and contraction of the packer; resilient means acting between the body and said arcuate shims to urge the shims outwardly into engagement with the sealing segments and at the same time to move the segments radially outwardly from the body; and stop means, carried by the body, for limiting said radially outward movement of the sealing segments.

2. A free piston for lifting fluid in a well tubing comprising, in combination, a body having a passageway for fluid therethrough; valve means in the body for controlling flow of fluid therethrough; an expansible packer on the body, said packer including an outer sealing assembly comprising a plurality of T-shaped arcuate sealing segments surrounding the body and arranged in interlocking relationship, said segments being mounted for movement radially of the body and having surfaces for sealably engaging the inner surface of said well tubing, and a separate inner back-up assembly comprising a plurality of arcuate shims bridging the gaps between adjacent ones of the sealing segments, said shims having their outer surfaces shaped to conform to and engage substantially the entire inner surfaces of said sealing segments; resilient means between the body and shims urging said shims radially outwardly from the body into said engagement with the inner surfaces of said sealing segments and at the same time acting to move the sealing segments radially outwardly from the body into sealing engagement with the well tubing.

3. A free piston for lifting fluid in a well tubing comprising, in combination a body having a passageway for fluid therethrough; valve means in the 'body operable to control flow of fluid therethrough; a radially expansible packer on the body, said packer including an outer sealing assembly comprising a plurality of interlocking arcuate sealing segments mounted for limited movement radially of the body and having labyrinth type seals extending substantially the full length of their outer faces for sealably engaging the inner surface of the well tubing, each of said sealing segments having a head portion and a stem portion with adjacent ones of the segments having their head portions and stem portions facing in opposite directions, and a separate inner back-up assembly comprising a plurality of arcuate shims carried by the sealing segments overlying and bridging the gaps between the longitudinal edges of adjacent ones of the segments; resilient means acting between the body and shims to move the shims outwardly into engagement with the sealing segments and in turn to move the sealing segments radially outwardly from the body into sealing engagement with the inner surface of the well tubing; and stop means, carried by the body, for limiting said radially outward movement of the sealing segments.

4. A free piston for lifting fluid in a #well tubing comprising, in combination, a body having a passageway for fluid therethrough; valve means in the body operable to control flow of fluid therethrough; a radially expansible packer on the body, said packer including an outer sealing assembly comprising a plurality of arcuate sealing segments mounted for. limited movement radially of the body and having their outer faces shaped to conform to and sealably engage the inner surface of the well tubing, each of said sealing segments having a head portion and an integral axially extending stem portion, adjacent onesof the segments having their head portions and stem portions facing in opposite'directions with the lateral edges of the head portions of adjacent segments overlapping at all times and the longitudinal edges of the stem and head portions of adjacent segments being spaced apart when the packer is expanded, and an inner back-up assembly between the body and sealing segments, said back-up assembly including a plurality of arcuate shims carried by the sealing segments overlying and slidably bridging the gaps between the longitudinal edges of adjacent ones of the segments, each of said shims having surfaces on their outer faces for sealably engaging the inner surfaces of adjacent ones of said sealing segments; spring means between the body and shims urging the shims radially outwardly from the body into engagement with said inner surfaces of the sealing segments and at the same time acting to move the sealing segments radially outwardly from the body into sealing engagement with the Well tubing;'and stop means on the body limiting the radially outward-movement of the sealing segments.

5. A free piston according to claim 4 further characterized in that said sealing surfaces on the sealing segments extend substantially the full length of the outer faces of the head and stem portions of the segments and comprise a plurality of alternate transverse lands and grooves formed along the head and stem portions of the segments. i

6. A free piston according to claim 4 further characterized in that said arcuate shims are sized to extend substantially the length of the sealing segments and to extend substantially the distance between the longitudinal axes of adjacent ones of the sealing segments. when the packer is contracted.

7. A free piston for lifting fluid in a well tubing comprising, in combination, a body having a passageway for fluid therethrough; valve means having parts cooperating with the body operable to selectively prevent and permit flow of fluid through the body; an expansible packer on the body, said packer including an outer sealing assembly comprising a plurality of T-shaped interlocking sealing segments mounted for limited movement radially of the body and having labyrinth type seals extending substantially the length of their outer faces shaped to engage and form a seal with the inner surface of the well tubing, and a separate inner back-up assembly comprising a plurality of arcuate shims interposed between the body and said sealing segments, the area of the outer surfaces of each of said shims being substantially equal to the area of the inner surfaces of each of said sealing segments and the several shims being positioned to overlie and bridge gaps between longitudinal edges of adjacent ones of the sealing segments; resilient means between the body and said shims acting to urge each of said shims radially outwardly from the body into engagement with the adjacent ones of the sealing segments and in turn to move the segments radially outwardly from the body into sealing engagement with the inner surface of the well tubing; and stop means on the body limting said radially outward movement of the sealing segments.

8. A free piston according to claim 7 further characterized in that each of said shims is positioned with its longitudinal axis parallel and at equal distances from the longitudinal axes of adjacent ones of the sealing segments.

9. A free piston according to claim 8 further characterized in that said resilient means is provided by a plurality of spring means, each of said spring means bearing against the body at one of its ends and bearing against a shim at the other of its ends at substantially the mid point of the longitudinal axis of such shim.

References Cited in the file of this patent UNITED STATES PATENTS 350,094 Lang Sept. 28, 1886 2,642,002 Knox et a1, June 16, 1953 2,762,310 Eklund Sept. 11, 1956 2,937,598 Brown May 24, 1960 

1. A FREE PISTON COMPRISING, IN COMBINATION, A BODY HAVING A PASSAGEWAY FOR FLUID THERETHROUGH; VALVE MEANS IN THE BODY FOR CONTROLLING FLOW OF FLUID THERETHROUGH; AN EXPANSIBLE PACKER ON THE BODY, SAID PACKER INCLUDING AN OUTER SEALING ASSEMBLY COMPRISING A PLURALITY OF INTERLOCKING SEALING SEGMENTS MOUNTED FOR LIMITED MOVEMENT RADIALLY OF THE BODY, SAID SEALING SEGMENTS HAVING SPACES BETWEEN THEIR ADJACENT LONGITUDINAL EDGES WHEN THE PACKER IS EXPANDED, AND A SEPARATE INNER BACK-UP ASSEMBLY INTERPOSED BETWEEN SAID BODY AND SAID SEALING SEGMENTS, SAID BACK-UP ASSEMBLY COMPRISING A PLURALITY OF ARCUATE SHIMS HAVING SURFACES SHAPED TO CONFORM TO THE INNER SURFACES OF SAID SEALING SEGMENTS, THE SEVERAL SHIMS BEING ARRANGED SO THAT EACH SHIM OVERLIES AND SEALABLY BRIDGES SAID SPACE BETWEEN ADJACENT ONES OF THE SEALING SEGMENTS DURING EXPANSION AND CONTRACTION OF THE PACKER; RESILIENT MEANS ACTING BETWEEN THE BODY AND SAID ARCUATE SHIMS TO URGE THE SHIMS OUTWARDLY INTO ENGAGEMENT WITH THE SEALING SEGMENTS AND AT T HE SAME TIME TO MOVE THE SEGMENTS RADIALLY OUTWARDLY FROM THE BODY; AND STOP MEANS, CARRIED BY THE BODY, FOR LIMITING SAID RADIALLY OUTWARD MOVEMENT OF THE SEALING SEGMENTS. 